The proposed experiments will examine an effect reported by Clement, Feltus, Kaiser, and Zentall (2000) in which a preference was found for stimuli that followed greater effort over those that followed less effort. When such effects are found in humans they are attributed to cognitive dissonance, the discrepancy between beliefs and behavior. Clement et al. interpreted this behavior as a form of contrast, in which stimuli that follow greater effort appear to have more value when compared to the aversive event that preceded it. However, their design does not rule out an account based on delay to reinforcement. The first set of proposed experiments will distinguish experimentally between contrast and delay reduction accounts. The next proposed experiment will examine whether a shift in food preference can result from requiring greater effort to obtain it, an application that could be used in treating eating disorders, such as obesity. A final experiment will examine whether a direct manipulation of hedonic state can produce a similar effect. Autism centers in the United States are applying this research to behavior management plans (how effort and subject reward value are related). This model is also used to study risk-taking and gambling behavior. [unreadable] [unreadable] [unreadable]